Cultivar Transitions in Kiwifruit and Associated Shifts in Bacterial Canker Pathogen Populations in Korea

Bacterial canker caused by Pseudomonas syringae pv. actinidiae (Psa) is one of the most destructive diseases affecting kiwifruit production worldwide. In Korea, the composition of cultivated kiwifruit cultivars has changed substantially over the past two decades. This study examined whether long-term transitions in host cultivar composition were associated with changes in pathogen lineage prevalence. National records of cultivar acreage, pathogen surveillance data, and observations of cultivar-dependent disease expression were analyzed. When production was dominated by the hexaploid cultivar ‘Hayward’, bacterial canker outbreaks were sporadic and mainly associated with Psa biovar 2. Following the rapid expansion of yellow-fleshed Actinidia chinensis cultivars in the early 2000s, Psa biovar 3 increased markedly and eventually became the dominant lineage nationwide. Greenhouse inoculation assays and field observations further revealed cultivar-dependent differences in disease expression. These results suggest that host cultivar composition may influence pathogen population structure at the productionsystem scale.